Continuous flow heaters in which the medium to be heated, being in a domestic situation generally water, is heated in a flow pipe forming at least part of a conduit leading from one part of an appliance to another may comprise a tubular heater element which includes a jacket tube forming the tubular outer casing of the tubular heater element. The tubular heater element and the pipe may be in the form of a one-piece hollow member, as disclosed for example in German published specification (DE-AS) No. 22 18 796. Depending on the requirements encountered in a practical situation, the flow pipe and the jacket tube of the tubular heater element may be of different cross-sections, wherein the cross-sectional configuration involved may differ from a circular configuration, being for example elliptical.
Alternatively, a continuous flow heater may comprise the pipe for carrying the flow of fluid, such as water, and a tubular heater body which is joined thereto as by soldering or by another form of thermal bridge, for example a common mounting plate which is thus connected to both the through-flow pipe and the tubular heater body.
However, those alternative forms of construction tend to suffer from the same disadvantages, as follows:
At least half the heat generated by the tubular heater member, often the amount of heat involved is greater than half depending on the particular design configuration involved, flows into the region of the through-flow pipe which is above the centre line thereof. As the transfer of heat to a vapour-air space is poor, the fact that a substantial proportion of the heat generated by the tubular heater member flows into the part of the pipe which is above the centre line means that there is an increased amount of radiant heat lost from the pipe to the exterior. This correspondingly involves the loss of a considerable amount of thermal and accordingly electrical energy. In the case of continuous flow heaters, the heat requires to drive the column of water upwardly into a riser pipe produces a great amount of steam, which issues from the discharge opening of the riser pipe, and in so doing frequently generates unpleasant snorting noises. Experience with conventional coffee-making machines has indicated that it is often about one sixth of the amount of water introduced into the appliance that is converted into steam uselessly in that fashion. As less electrical energy is required for heating the water to boiling temperature than for vaporising the boiling water, there is a high level of energy consumption which is no longer acceptable under present-day conditions.
The aim therefore is to provide a construction in which the flow of heat from the tubular heater member to the through-flow pipe can be improved and the amount of energy radiated to the exterior from the tubular heater member can be reduced, and in which the greater part of the amount of heat given off to the through-flow pipe by the tubular heater member is transmitted from below to the column of water therein so that the formation of steam for example in a coffee making machine occurs at the bottom of the through-flow pipe, in the form of small bubbles which provide a corresponding upward force for driving the column of water out of the riser pipe, while avoiding a surge discharge of steam out of the steam space above the surface of the water.